Method for identification of base stations and for checking measurement values of an observed time difference between transmissions from base stations

ABSTRACT

A method for identification of transceiver devices in a radio communication network, includes the steps of pre-identifying transceiver devices, judging that there is an ambiguous result obtained in the pre-identification, and verifying the ambiguous result by identifying the transceiver devices based on real time difference (RTD) values between the transceiver devices. Also the method may include checking measurement values of an observed time difference (OTD) obtained at a mobile transceiver device operated within a radio communication network constituted by transceiver devices, wherein the checking is based on real time difference values between the transceiver devices. Thus, an improved method is obtained for mobile station location determination and/or for taking handover decisions as well as a way of verifying the reliability of obtained measurement results.

FIELD OF THE INVENTION

The present invention relates to a method for identification oftransceiver devices and for checking measurement values of an observedtime difference.

BACKGROUND OF THE INVENTION

Recently, development of communication networks and in particular ofradio communication networks has made considerable progress. Forexample, the GSM network and its successors such as the GPRS and/or UMTSnetworks find increasing attention.

Basically, radio communication networks are constituted by transceiverdevices also known as base transceiver stations BTS. A mobiletransceiver station also known as mobile station MS (according to GSM)and/or user equipment UE (according to UMTS) communicates via the radiointerface (air interface) with the transceiver devices constituting thenetwork. Of course, the transceiver devices are controlled by othernetwork elements of a higher hierarchy which, however, are omitted fromthe description in this case as this is considered to be not essentialto the invention to be described.

Generally, a mobile station MS may move and/or roam within the radiocommunication network. In this connection, there may arise a situationin which a mobile station MS leaves the coverage area of a serving basetransceiver station BTS and is handed over to a new base transceiverstation BTS.

To this end, a knowledge of the transceiver stations surrounding themobile station and/or a serving transceiver station is required in orderto take a proper decision on where to handover the moving mobilestation. Correspondingly, a knowledge of the mobile station's positionwithin the network is required.

According to one principle, the required knowledge is obtained bymeasurements performed by e.g. the mobile station itself, which measuresthe observed time difference OTD between signals received at the mobilestation from a pair of transceiver stations BTS, e.g. between acurrently serving base transceiver station and a respective other basetransceiver station.

This is known as OTD method and described in literature in detail.Briefly summarized, e.g. in GSM phase 2 systems, support forpseudo-synchronous handover is compulsory. In a pseudo-synchronoushandover, the mobile station MS will keep the timing values for thesurrounding base transceiver stations BTSs in order to bepre-synchronized to the new BTS upon handover. To obtain thissynchronization, the MS must calculate and/or measure an Observed TimeDifference (OTD) between signals received from the serving BTS and theother BTSs. Each BTS must maintain a Real Time Difference, RTD, betweenitself and a respective one of its neighboring base stations. Whenhandover is performed, the RTD is supplied to the mobile station MS,which with the knowledge of the RTD and OTD can calculate the TimingAdvance needed to synchronize with the new BTS, and go directly intosynchronization. Further details of this procedure are defined in GSMspecification 05.10.

There exists also a modified OTD scheme, which is known as EnhancedObserved Time Difference (E-OTD). In brief, the E-OTD positioning methodis based on signal measurements made by the mobile station (MS) andlocation measurement units (LMUs), which are essentially stationarymobiles of known position. To calculate the position of the mobile, thenetwork uses three parameters: observed time difference (OTD), real timedifference (RTD), and geometric time difference (GTD). GTD is derivedfrom OTD and RTD, and gives the mobile's position. The OTD measurementsare time intervals measured by a mobile station MS between receivedsignals originating from two different base stations. Because the GSMnetwork is not synchronized, the network measures the RTD, which is therelative synchronization difference between the two base stations. Toobtain accurate triangulation, OTD and RTD measurements of at leastthree geographically distinct base stations are needed. Based on themeasured OTD and RTD values, the location of the MS can be calculated.The position of the MS is determined by deducing the geometricalcomponents of the time delays (GTD) to a mobile station MS from the basestations.

E-OTD as a mobile station location method in GSM requires that themobile is able to receive at least two neighboring base stations (inaddition to the currently serving BTS). According to GSM specification04.31, the mobile station can identify the neighbor BTS by using:

-   1) an index referring to the BTS listed in the Measure Position    Request component,-   2) an index referring to the BTS listed in the BCCH allocation list    (System Information Neighbor Lists) of the serving BTS,-   3) cell identity CI and location area code LAC,-   4) base station identity code BSIC value and broadcast control    channel BCCH carrier information,-   5) 51-Multiframe offset and BCCH carrier. Correct identification of    the neighbor base station is of outmost importance for successful    and accurate location.

Nevertheless, there may arise situations in which the above listedmeasures will not be sufficient to properly identify a base transceiverstation and/or transceiver device constituting the radio communicationnetwork without doubt.

Stated in other words, BSIC and BCCH carrier are not a unique way toidentify a base station. Theoretically, a proper network planning shouldensure that it is not possible for a mobile station to receive signalsfrom two or more different base stations with the same BSIC and BCCHcarrier combination, and that based on a serving base station it isevident, which neighbor base station (with a certain BSIC and BCCHcarrier combination) the mobile has measured.

However, in reality it is possible that the same BSIC and BCCH carriercombination repeats itself so tightly (i.e. spatially close to eachother within the network) that situations arise in which it is ambiguous(not clear) which neighbor base station was measured. Since mobilestations mainly use the information of BSIC and BCCH carrier forneighbor base station identification, there may arise a problem.

-   Likewise, when a neighbor base station is identified with a    51-Multiframe offset and BCCH carrier, the same problem can arise if    a frequency reuse pattern is tight, and 51-Multiframe offsets happen    to be the same.

In some cases it is also possible that two different base stations sharethe same cell identity CI and location area code LAC. This can happen ifInter-PLMN HO feature is in use (PLMN=Public Land Mobile Network,HO=Handover). Inter PLMN HO feature means basically that a basetransceiver station BTS can have neighbor cells which belong todifferent countries and/or operators and MS can make a handover to thosecells, as it is the case e.g. in international roaming near countryborders.

FIG. 1 schematically illustrates such a situation. A serving BTS alsoreferred to as reference BTS is not shown in FIG. 1. Rather, there isshown the mobile station MS trying to identify its surrounding basetransceiver stations, i.e. potential neighbors BTS1, BTS2 to which e.g.a handover HO could be performed. As shown in FIG. 1, the mobile stationMS receives identical information concerning the BSIC for the two basetransceiver stations, i.e. BSIC1=BSIC2. Also, the BCCH information forBTS1 and BTS2 is identical (BCCH1=BCCH2), and also the offsets, i.e.51-multiframe offsets offset1/offset2 are identical. In such asituation, it is evident that identifying said transceiver devices (whene.g. accomplished based on respective broadcast control channel BCCHinformation of said transceiver devices and/or on a respective basestation identity code BSIC of said transceiver devices) leads to anambiguous result since it is evident to be judged that the transceiverdevices can no longer be distinguished from each other.

In addition to an identification problem, there can be situations, whenthe E-OTD value reported by the mobile station can be corrupted becausethe mobile station performs for some reason (e.g. bad radio environment)very poor measurements, or because for other reasons the measurementinformation from the mobile station is bad.

SUMMARY OF THE INVENTION

Hence, in view of the above situations, it is an object of the presentinvention to provide a method for identification of transceiver devicesand for checking measurement values of an observed time difference whichare respectively free from the above described drawbacks and problems.

According to the present invention, this object is for example achievedby a method for identification of transceiver devices constituting aradio communication network, said method comprising the steps ofpre-identifying said transceiver devices, judging that there is anambiguous result obtained in said pre-identification, and verifying saidambiguous result by identifying said transceiver devices based on realtime difference RTD values between said transceiver devices.

According to advantageous further developments of said method,

-   -   said pre-identifying is accomplished based on respective        broadcast control channel BCCH information of said transceiver        devices,    -   said pre-identifying is (additionally or alternatively)        accomplished based on a respective base station identity code        BSIC of said transceiver devices,    -   it is judged that there is an ambiguous result obtained in said        pre-identification, if the transceiver devices can no longer be        distinguished from each other,    -   the transceiver devices can no longer be distinguished from each        other if the respective BCCH information of said transceiver        devices are identical.    -   the transceiver devices can no longer be distinguished from each        other, if (additionally or alternatively) the respective base        station identity code BSIC of said transceiver devices are        identical,    -   said verifying is based on a relation between an observed time        difference OTD at a mobile transceiver device, the real time        difference RTD of transmission times between said transceiver        devices constituting said radio communication network, and the        geometric time difference GTD being due to different propagation        times between the mobile transceiver device and the transceiver        devices constituting said radio communication network, the        relation being expressed as OTD=RTD+GTD,    -   said verifying comprises estimating a minimum GTD_(expected,min)        and a maximum GTD_(expected,max) value of said geometric time        difference GTD, deriving, based on said observed time difference        OTD and said estimated maximum and minimum geometric time        difference GTD, a respective minimum RTD_(expected,min) and a        maximum RTD_(expected,max) expected value of said real time        difference RTD such that        RTD_(expected,min)=OTD−GTD_(expected,max),        RTD_(expected,max)=OTD−GTD_(expected,min),    -   said verifying further comprises comparing known real time        difference RTD values of said transceiver devices with said        range of expected real time difference values        RTD_(expected,min), RTD_(expected,max), and if the real time        difference value of the transceiver device is found to be within        said range of expected real time difference values, identifying        this transceiver device as an unambiguous neighbor transceiver        device to a reference transceiver device.

Furthermore, according to the present invention the above object is forexample achieved by a method for checking measurement values of anobserved time difference OTD obtained at a mobile transceiver deviceoperated within a radio communication network constituted by transceiverdevices, wherein said checking is based on real time difference RTDvalues between said transceiver devices.

According to advantageous further developments of said method,

-   -   said checking is based on a relation between an observed time        difference OTD at a mobile transceiver device, the real time        difference RTD of transmission times between said transceiver        devices constituting said radio communication network, and the        geometric time difference GTD being due to different propagation        times between the mobile transceiver device and the transceiver        devices constituting said radio communication network, the        relation being expressed as OTD=RTD+GTD,    -   said checking comprises estimating a minimum GTD_(expected,min)        and a maximum GTD_(expected,max) value of said geometric time        difference GTD, obtaining, based on said real time difference        RTD and said estimated maximum and minimum geometric time        difference GTD, a respective minimum OTD_(expected,min) and a        maximum OTD_(expected,max) expected value of said observed time        difference OTD such that        OTD_(expected,min)=RTD+GTD_(expected,max),        OTD_(expected,max)=RTD+GTD_(expected,min),    -   said checking further comprises comparing measured observed time        difference OTD values with said range of expected observed time        difference values OTD_(expected,min), OTD_(expected,max), and if        the observed time difference value at the mobile transceiver        device is found to be within said range of expected observed        time difference values, this measurement value is accepted,        while otherwise it is rejected.        Further, according to advantageous further developments of both        of the above mentioned methods,    -   1. said estimation of maximum and minimum geometric time        difference GTD is based on information about the location of the        mobile transceiver device already available in the communication        network,    -   2. said already available information about the location of the        mobile transceiver device is obtained, in GSM communication        systems, using Cell Identity CI and/or Cell Identity CI and        Timing Advance TA values of the mobile transceiver device, and,        in UMTS communication systems, using Cell Identity (CI) and/or        Cell Identity CI and Service Area Identifier SAI and/or Round        Trip Time (RTT) values,    -   3. said estimation of maximum and minimum geometric time        difference GTD_(max), GTD_(min) further comprises setting the        maximum GTD value GTD_(max) equal to the distance between the        two transceiver devices divided by the speed of radio waves, and        setting the minimum GTD value GTD_(min) equal to the negative of        the distance between the two transceiver devices divided by the        speed of radio waves,    -   4. said estimation of maximum and minimum geometric time        difference GTD_(max), GTD_(min) further comprises performing the        estimation as stated in the item 1 or 2 above, performing the        estimation as stated in the item 3 above, and selecting for the        maximum GTD_(max) the value of the estimates obtained in the two        steps above which is smaller, and selecting for the minimum        GTD_(min) the value of the estimates obtained in the two steps        above which is larger.

Also, according to the present invention, the above object is achievedby a device for identification of transceiver devices constituting aradio communication network, the device being adapted to carry out themethod according to any of the previously described method aspects, aswell as by a device for checking measurement values of an observed timedifference OTD obtained at a mobile transceiver device operated within aradio communication network constituted by transceiver devices, thedevice being adapted to carry out the method according to any of thepreviously described method aspects.

Accordingly, by virtue of the present invention being implemented thefollowing advantages can be achieved:

-   easy implementation in existing products can be realized,-   possible to implement without any standards changes,-   no hardware changes needed,

a solution for base station identity ambiguity problem with enhancedperformance due to “sanity” checks of measurement values.

Thus, the present invention offers an improved method for mobile stationlocation determination and/or for taking handover decisions as well as away of verifying the reliability of obtained measurement results.

The above and further objects, features, and advantages of the presentinvention will be more readily understood upon referring to theaccompanying drawings in conjunction with the subsequent description.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 illustrates a situation in a radio communication network in whichno unambiguous identification of base transceiver stations is possiblebased on BSIC and/or BCCH and/or 51-multiframe offset information;

FIG. 2 illustrates a basic arrangement for explaining the estimation ofan expected maximum/minimum GTD value, and

FIG. 3 shows a modified arrangement for explaining the estimation of anexpected maximum/minimum GTD value.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention is subsequently described in detail with regard tothe accompanying drawings.

According to the present invention, it is proposed that the Real TimeDifference (RTD) values that describe the transmission time differencesbetween base stations, and that are needed for E-OTD location, will beused on one hand to distinguish between ambiguous identificationparameters, and on the other hand to perform sanity checks (reliabilitychecks) for reported measurements.

For example, a Serving Mobile Location Center (SMLC) as a network nodewhich receives E-OTD measurements from the mobile station, knows RTDvalues, and calculates location estimates. Thus, the SMLC can easilyalso use RTD values according to the proposed method. The SMLC may be aseparate network node or be part of e.g. a base station controller, amobile services switching center or the like, as long as its requiredfunctionality is implemented.

Nevertheless, the required functionality could e.g. also implemented inthe mobile station MS itself provided that the necessary data such asRTD are supplied thereto.

Basically, in connection with E-OTD location, the mobile station (MS)either reports Observed Time Difference (OTD) measurement results to theServing Mobile Location Center SMLC, or, alternatively, the mobile canuse measurements itself to calculate its own position. This has beenspecified in GSM standards (e.g. Location Services Stage 2 descriptionGSM 03.71).

The well-known equation relating OTD and RTD is:OTD=RTD+GTD  (1)where OTD is the measured Observed Time Difference between the arrivalsof signals from the reference base station (BTS) and the neighbor basestation. OTD refers thus to a pair of base stations comprising thereference base station (e.g. the currently serving base station for themobile station) and a potential neighbor base station. RTD is the RealTime Difference, i.e. the transmission time difference between the basestation pair (reference and neighbor) in question. Geometric TimeDifference (GTD) is due to different propagation times (differentdistances) between the mobile and two base stations. GTD includes actualinformation about location:GTD=[d(MS,BTS1)−d(MS,BTS2)]/c  (2)where d(MS, BTSx) is the distance between the MS and the BTSx, and c isthe speed of radio waves. (It is to be noted that in FIGS. 2 and 3 aneighbor base transceiver station BTS is denoted by BTS_A, while areference base transceiver station is denoted by BTS_B.)Solving Base Station Ambiguity

According to the present invention, in order to solve an ambiguoussituation in which the identities of base stations can not be determinedon the basis of e.g.

BSIC/BCCH etc., an estimate of the value of GTD, GTD_(expected), isformed. It will normally be a range, i.e. it consists of a minimumGTD_(expected,min) and maximum value GTD_(expected,max), as subsequentlyexplained.

Determination of Expected GTD

One way to estimate the expected GTD comes from the fact that themagnitude of GTD (in distance units, e.g. multiplied by speed of radiowaves) can not be larger than the distance between the reference andneighbor base stations. This is obvious from equation (2) above andgeometry.

FIG. 2 shows an example situation for determining the minimum andmaximum value of GTD_(expected). In FIG. 2 it is assumed that the basetransceiver stations BTS_A (reference) and BTS_B (neighbor) have a“straight” radio path between them and that the mobile station MS has aposition somewhere on this straight radio path “line of sight”.

So, if the mobile station is exactly in the middle between the two basetransceiver stations, then GTD=0, since the mobile station receives thesignals transmitted from the base stations simultaneously (under theassumption that BTS_A, BTS_B transmit synchronously). If, however, themobile station is at the position of the base station BTS_A (neighbor),the GTD is a minimum (negative value), while if the mobile station is atthe position of the base station BTS_B (reference), the GTD is a maximum(positive value).

Note that the signs depend on definition of GTD, and in FIG. 2, GTD isassumed to be defined as[d(MS,neighbor)−d(MS,reference)]/c.

Thus one way to set GTD_(expected) isGTD _(expected,min)=−distance(referenceBTS, neighborBTS)/c andGTD _(expected,max)=distance(referenceBTS, neighborBTS)/c.

A further approach for determination of minimum and maximum values ofGTD_(expected) is illustrated in FIG. 3. This approach is based on thataccording to GSM specifications, in each location services transaction,an initial location estimate is obtained based on Cell Identity CIand/or Timing Advance TA (see e.g. GSM 03.71). That is, an initialestimate may be obtained based on CI alone or on CI and TA incombination. When the initial estimate with its related confidence areaare known, it can be used to estimate GTD even more accurately. In thirdgeneration UMTS systems, Cell Identity (CI) and/or Service AreaIdentifier (SAI) and/or Round Trip Time (RTT) values can be usedsimilarly. That is, CI, and/or CI and SAI, and/or CI and SAI and RTT,and/or CI and RTT can be used. Just as an example, the term locationservices transaction as used herein refers to a normal GSM locationservices event, which can be a Mobile-Terminated Location Request(MT-LR), Mobile-Originated Location Request (MO-LR), or Network-InducedLocation Request (NI-LR) (e.g. in LCS system description GSM 03.71).

It is assumed that as shown in FIG. 3, the initial location estimate andits confidence area define an area D where the mobile station MS (notshown in FIG. 3) is with a certain probability level x. Then minimum andmaximum values of GTD_(expected) can be found at those points within thearea D, where the signed distance difference to the reference andneighbor base stations is minimum and maximum, respectively.

In the example of FIG. 3, GTD_(expected,max) can be found in the pointA, i.e. there [d(XY,neighbor)−d(XY,reference)]/c has its maximum value,when restricting the point XY to be within the boundaries of the area D.Correspondingly, GTD_(expected,min) can be found in the point B. It isto be noted that above a point XY is intended to define a location byits coordinates x, y, so that point A is defined as x_(A), y_(A), andpoint B as x_(B), y_(B).

It is also possible to perform and combine both estimations as describedin FIGS. 2 and 3. Then, for estimate of the minimum GTD, there can beselected the value that is larger (i.e. has smaller absolute value) ofthe two minimum GTD estimates. Correspondingly, for estimate of themaximum GTD, there can be selected the value that is smaller of the twomaximum GTD estimates. This leads to a smallest interval betweenGTD_(min) and GTD_(max) being estimated for use in the furtherprocessing.

Herein before, different ways to obtain the expected GTD value rangehave been described. Once the interval of expected GTD values isobtained, these can be used according to the present invention in orderto solve an ambiguous base station identification.

To this end, using the measured OTD value and equation (1), an expectedRTD value, RTD_(expected), is calculated. Again it will be usually be arange of values with minimum RTD_(expected,min) and maximumRTD_(expected,max).RTD _(expected,min) =OTD−GTD _(expected,max)  (3)RTD _(expected,max) =OTD−GTD _(expected,min)  (4)

For identification purposes, the expected RTD range is compared with theknown RTD values (i.e. those known by the network and/or the SMLCentity).

Let's consider a situation, when a neighbor base station is identifiedwith BSIC and BCCH carrier combination, but due to too tight frequencyreuse, there are two possible base stations with the same BSIC and BCCHcarrier combination (as explained above in connection with FIG. 1).Stated in other words, according to the method for identification oftransceiver devices constituting a radio communication network, saidtransceiver devices are pre-identified based on BSIC and/or BCCHinformation, and it is judged that there is an ambiguous result obtainedin said pre-identification.

Then, further according to the present invention, the expected RTD rangeis formed [RTD_(expected,min) . . . RTD_(expected,max)], for bothpossible (neighbor) base stations, and it is checked whose real RTDvalue is within the range.

More precisely, an expected RTD range is formed for each potentialneighbor base station or for one of them in relation to the referencebase station (currently serving BTS). Then, the real RTD values arecompared to the RTD range, in order to determined, whether one of theRTD values of the neighbor base stations is within the range.

If one of them is, then that's the right base station. If both are, thenthe ambiguity can not be solved (it is possible that the two basestations have almost the same RTD value relative to the reference basestation). However, the probability for this situation is not too high.

Sanity Check

Furthermore, performing a sanity check for the measured OTD value can bedone again by forming GTD_(expected,min) and GTD_(expected,max).

Then by knowing the real RTD value, an expected OTD range is formed:OTD _(expected,min) =RTD+GTD _(expected,min)  (5)OTD _(expected,max) =RTD+GTD _(expected,max)  (6)

If the measured OTD value is within the range [OTD_(expected,min) . . .OTD_(expected,max)], it can be concluded that the measurement iscorrect, otherwise the measurement result is rejected.

It is to be noted that RTD values can be determined by usingmeasurements from Location Measurement Units LMU. LMUs report their(actually OTD) measurements to the SMLC, that calculates the RTD valuesand maintains them. SMLCs can also exchange RTD information between eachother. GSM Location Services LCS specifications allow the SMLC torequest the LMUs to report periodically, or when the measurement valueshave changed by more than a certain limit. Thus it is possible for theSMLC to know all the time the RTD values in the network.

Furthermore, it is to be noted that a knowledge of the area D (FIG. 3)can be derived based on available information (already known in thenetwork) about the location of the mobile transceiver device and theuncertainty of the location. For example in GSM, in connection with alocation transaction, Cell Identity CI and Timing Advance TA values areknown. Based on them an arc (like in FIG. 3) can be defined inside whichthe MS is present with a certain probability. Basically it is possibleto apply any of the well known mathematical approaches for finding aminimum and maximum value for a function (in this case the function isGTD=[distance(XY, BTS1)−distance(XY, BTS2)]/c, where XY is a point) withcertain limits set for the variable of the function (in this case XY asthe expected location).

For example, if the BTSs are outside the area D, then the minimum andmaximum are found at the boundary of the area D. In the case when thearea D is obtained using CI and/or CI and TA, there are well defineddefinitions for the boundaries. Then we set the point XY to be on theboundary and find the points XY where GTD gets its maximum and minimumvalues (A and B in FIG. 3, respectively). The point XY, i.e. A and B inFIG. 3, respectively, where this maximum and minimum values are foundcan be called maximum and minimum. If one or both of the BTSs are in thearea D, then the finding of minimum and maximum for GTD is basically thesame, except that now XY can also be inside the area. A brute-forceapproach can be just to divide the area D into a grid and then gothrough each point XY to find minimum and maximum.

Although herein above the present invention has mainly been describedwith reference to the method, it is to be understood that of course alsocorrespondingly adapted devices are concerned by the present invention.That is, the present invention also concerns a device for identificationof transceiver devices constituting a radio communication network, thedevice being adapted to carry out the method according to any of thepreviously described method aspects, as well as a device for checkingmeasurement values of an observed time difference OTD obtained at amobile transceiver device operated within a radio communication networkconstituted by transceiver devices, the device being adapted to carryout the method according to any of the previously described methodaspects.

Accordingly, as has been described above, the present invention concernsa method for identification of transceiver devices BTS_A, BTS_Bconstituting a radio communication network, said method comprising thesteps of pre-identifying said transceiver devices, judging that there isan ambiguous result obtained in said pre-identification, and verifyingsaid ambiguous result by identifying said transceiver devices based onreal time difference RTD values between said transceiver devices. Also,the present invention concerns a method for checking measurement valuesof an observed time difference OTD obtained at a mobile transceiverdevice operated within a radio communication network constituted bytransceiver devices, wherein said checking is based on real timedifference RTD values between said transceiver devices. Thus, thepresent invention offers an improved method for mobile station locationdetermination and/or for taking handover decisions as well as a way ofverifying the reliability of obtained measurement results.

Although the present invention has been described herein above withreference to its preferred embodiments, it should be understood thatnumerous modifications may be made thereto without departing from thespirit and scope of the invention. It is intended that all suchmodifications fall within the scope of the appended claims.

1. A method for identification of transceiver devices constituting aradio communication network, said method comprising pre-identifying saidtransceiver devices, judging that there is an ambiguous result obtainedin said pre-identification, and verifying said ambiguous result byidentifying said transceiver devices based on real time differencevalues between said transceiver devices.
 2. A method according to claim1, wherein said pre-identifying is accomplished based on respectivebroadcast control channel broadcast control channel information of saidtransceiver devices.
 3. A method according to claim 1, wherein saidpre-identifying is accomplished based on a respective base stationidentity code of said transceiver devices.
 4. A method according toclaim 1, wherein it is judged that there is an ambiguous result obtainedin said pre-identification, if the transceiver devices can no longer bedistinguished from each other.
 5. A method according to claim 4, whereinthe transceiver devices can no longer be distinguished from each otherif the respective broadcast control channel information of saidtransceiver devices are identical.
 6. A method according to claim 4,wherein the transceiver devices can no longer be distinguished from eachother, if the respective base station identity code of said transceiverdevices are identical.
 7. A method according to claim 1, wherein saidverifying is based on a relation between an observed time difference OTDat a mobile transceiver device, the real time difference RTD oftransmission times between said transceiver devices constituting saidradio communication network, and the geometric time difference GTD beingdue to different propagation times between the mobile transceiver deviceand the transceiver devices constituting said radio communicationnetwork, the relation being expressed asOTD=RTD+GTD.
 8. A method according to claim 7, wherein said verifyingcomprises estimating a minimum GTD_(expected,min) and a maximumGTD_(expected,max) value of said geometric time difference GTD,deriving, based on said observed time difference OTD and said estimatedmaximum and minimum geometric time difference GTD, a respective minimumRTD_(expected,min) and a maximum RTD_(expected,max) expected value ofsaid real time difference RTD such thatRTD _(expected,min) =OTD−GTD _(expected,max)RTD _(expected,max) =OTD−GTD _(expected,min).
 9. A method according toclaim 8, wherein said verifying further comprises comparing known realtime difference values of said transceiver devices with said range ofexpected real time difference values RTD_(expected,min.),RTD_(expected,max), and if the real time difference value of thetransceiver device is found to be within said range of expected realtime difference values, identifying this transceiver device as anunambiguous neighbor transceiver device to a reference transceiverdevice.
 10. A method according to claim 8, wherein said estimation ofmaximum and minimum geometric time difference is based on informationabout the location of the mobile transceiver device already available inthe communication network.
 11. A method according to claim 10, whereinsaid already available information about the location of the mobiletransceiver device is obtained, in Global System for Mobilecommunication systems, using Cell Identity and/or Cell Identity andTiming Advance values of the mobile transceiver device, and, inUniversal Mobile telecommunication systems, using Cell Identity and/orCell Identity and Service Area Identifier and/or Round Trip Time values.12. A method according to claim 8, wherein said estimation of maximumand minimum geometric time difference GTD_(max), GTD_(min) furthercomprises setting the maximum GTD value GTD_(max) equal to the distancebetween the two transceiver devices divided by the speed of radio waves,and setting the minimum GTD value GTD_(min) equal to the negative of thedistance between the two transceiver devices divided by the speed ofradio waves.
 13. A method according to claim 8, wherein said estimationof maximum and minimum geometric time difference GTD_(max), GTD_(min)further comprises estimating maximum and minimum geometric timedifference based upon information about the location of a mobiletransceiver device already available in the communication network;estimating maximum and minimum geometric time difference by setting themaximum GTD value GTD_(max) equal to the distance between the twotransceiver devices divided by the speed of radio waves, and setting theminimum GTD value GTD_(min) equal to the negative of the distancebetween the two transceiver devices divided by the speed of the radiowaves, and selecting for the maximum GTD_(max) the value of theestimates obtained in the two steps above which is smaller, andselecting for the minimum GTD_(min) the value of the estimates obtainedin the two steps above which is larger.
 14. The method according toclaim 1, further comprising checking measurement values of an observedtime difference obtained at a mobile transceiver device operated withina radio communication network constituted by transceiver devices,wherein said checking is based on real time difference values betweensaid transceiver devices.
 15. A method according to claim 14, whereinsaid checking is based on a relation between an observed time differenceOTD at a mobile transceiver device, the real time difference RTD oftransmission times between said transceiver devices constituting saidradio communication network, and the geometric time difference GTD beingdue to different propagation times between the mobile transceiver deviceand the transceiver devices constituting said radio communicationnetwork, the relation being expressed asOTD=RTD+GTD.
 16. A method according to claim 15, wherein said checkingcomprises estimating a minimum GTD_(expected,min) and a maximumGTD_(expected,max) value of said geometric time difference, obtaining,based on said real time difference and said estimated maximum andminimum geometric time difference, a respective minimumOTD_(expected,min) and a maximum OTD_(expected,max) expected value ofsaid observed time difference such thatOTD _(expected,min) =RTD+GTD _(expected,max)OTD _(expected,max) =RTD+GTD _(expected,min).
 17. A method according toclaim 16, wherein said checking further comprises comparing measuredobserved time difference values with said range of expected observedtime difference values OTD_(expected,min), OTD_(expected,max), and ifthe observed time difference value at the mobile transceiver device isfound to be within said range of expected observed time differencevalues, this measurement value is accepted, while otherwise it isrejected.
 18. A device for identification of transceiver devicesconstituting a radio communication network, the device configured to:pre-identify said transceiver devices; judge that there is an ambiguousresult obtained at said pre-identification; and verify said ambiguousresult by identifying said transceiver devices based on real timedifference values between said transceiver devices.
 19. The deviceaccording to claim 18, further configured to check measurement values ofan observed time difference obtained at a mobile transceiver deviceoperated within a radio communication network constituted by transceiverdevices, the device comprising a checking unit configured to perform acheck based on real time difference values between said transceiverdevices.
 20. A device for identification of transceiver devices,comprising means for pre-identifying transceiver devices in a radionetwork; means for judging that there is an ambiguous result obtained ina pre-identifying process; and means for verifying the ambiguous resultby identifying the transceiver devices based on real time differencevalues between the transceiver devices.
 21. The device according toclaim 20, further comprising: a checking means for performing a checkbased on real time difference values between at least two transceiverdevices, wherein an observed time difference is obtained at a mobiletransceiver device operated within a radio communication networkconstituted by transceiver devices.